U.S. patent number 10,689,189 [Application Number 16/209,245] was granted by the patent office on 2020-06-23 for external floating roof tank shell extension.
This patent grant is currently assigned to PHILLIPS 66 COMPANY. The grantee listed for this patent is PHILLIPS 66 COMPANY. Invention is credited to Jeff McBride, Paul J. Rady.
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United States Patent |
10,689,189 |
Rady , et al. |
June 23, 2020 |
External floating roof tank shell extension
Abstract
The invention relates to an inexpensive technique and procedure
to add storage capacity to existing hydrocarbon storage tanks that
have a double seal floating roof. The additional storage capacity
is obtained by installing an extension that is strong enough to
provide the upper seal of the double seal arrangement to maintain a
sealed vapor space that allows the roof to move higher within the
existing peripheral wall of the storage tank.
Inventors: |
Rady; Paul J. (Katy, TX),
McBride; Jeff (Houston, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
PHILLIPS 66 COMPANY |
Houston |
TX |
US |
|
|
Assignee: |
PHILLIPS 66 COMPANY (Houston,
TX)
|
Family
ID: |
70849958 |
Appl.
No.: |
16/209,245 |
Filed: |
December 4, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B65D
90/38 (20130101); B65D 88/42 (20130101); B65D
88/005 (20130101) |
Current International
Class: |
B65D
88/42 (20060101); B65D 90/38 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Vaughan; Jason L
Assistant Examiner: Kreiling; Amanda
Attorney, Agent or Firm: Phillips 66 Company
Claims
The invention claimed is:
1. A process for expanding the capacity of a floating roof
cylindrical tank for storing hydrocarbons comprising: providing a
cylindrical tank with a generally circular base having a periphery
extending fully around the circular base and generally cylindrical
peripheral wall extending vertically upward to a top edge and a
floating roof with two spaced apart seals arranged for sealing
contact against the generally cylindrical peripheral wall;
providing a plurality of brackets up to the top of the floating
roof where the brackets include pre-drilled holes for attaching
extension panels; providing a plurality of extension panels that
are each thinner and lighter weight than the generally cylindrical
peripheral wall up to the top of the floating roof where the
extension panels include pre-drilled holes to attach to the
brackets and to attach each panel to others of the plurality of
panels; providing a sealant between each bracket and the generally
cylindrical peripheral wall and attaching each bracket to the
generally cylindrical wall end to end so as to create a sealed
connection between the brackets and the generally peripheral wall
and to provide a structure for which the extension panels may be
attached to the generally cylindrical peripheral wall; providing a
sealant between each of the panels and the bracket and attaching
each of the panels to the bracket and to one another in an
overlapping arrangement where the panels overlap at least part of
the bracket and where at least part of each panel overlaps with
other panels with sealant between where they overlap such that when
the panels are attached to the brackets they form a generally
cylindrical wall extension extending upwardly from the generally
cylindrical wall such that the upper of the two seals on the
floating roof may move vertically with the floating roof and
maintain a sealed vapor space as the seal passes above the top edge
of the generally cylindrical peripheral wall and into contact with
the panel extensions sealed together and to the generally
cylindrical peripheral wall.
2. The process according to claim 1 wherein the top edge includes
an outwardly extending flange and the bracket is secured to the
outwardly extending flange.
3. The process according to claim 1 wherein the panels connect to
one another at overlapping joints and each bracket butts up against
brackets at each edge at butt joints such that the process includes
attaching the panels together such that the overlapping joints are
offset relative to the butt joints so that two such joints do not
coincide to weaken the seal of the floating roof storage tank.
4. The process according to claim 1 wherein the panels are attached
to one another by rivets.
5. The process according to claim 1 where the brackets and panels
are installed while hydrocarbons are stored in the floating roof
storage tank and no drilling or welding would be allowed to occur
that would be hazardous with hydrocarbons in such proximity to the
installation of the panel extension.
6. The process according to claim 1 where the peripheral wall has a
thickness and the panel extensions has a thickness and wherein the
step of providing the panel extensions includes selecting panel
extensions that are less than on fifth of the peripheral wall
thickness.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
None.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
None.
FIELD OF THE INVENTION
This invention relates to generally cylindrical liquid hydrocarbon
storage tanks and more particularly to large capacity liquid
hydrocarbon storage tanks for storing crude oil and hydrocarbon
products used in refineries and in petrochemical and fuel
transportation and distribution facilities.
BACKGROUND OF THE INVENTION
Generally cylindrical hydrocarbon storage tanks have been in use in
refineries for many years. These tanks have been used to store and
blend crude oils and intermediate hydrocarbon products for refining
and also to store finished fuels for distribution. One of the
safety advances for such storage tanks is the development of a
floating roof. One of the concerns in storing hydrocarbons is that
hydrocarbon vapors are, in many cases, flammable and, in some
cases, have a toxicity concern. The floating roof development has
reduced these concerns by reducing the volume of vapors in these
large storage tanks.
Basically, a floating roof comprises a roof that is separate from
the storage tank and floats on the liquid surface using flotation
pontoons or other flotation arrangement. The roof then rises and
falls with the volume of hydrocarbons. The vapor space is then
limited to the volume between the liquid surface and the underside
of the floating roof. To contain the vapors from the outside
atmosphere two or more seals are positioned around the periphery of
the floating roof to be in contact with the inside wall of the tank
to seal the small vapor space from the outside atmosphere and
prevent hydrocarbon releases. Typically, in such double seal
arrangements, a primary seal is located just above the liquid level
and a second seal is positioned above the primary seal by as much
as four feet, but typically between about 18 inches and up to about
36 inches above the primary seal.
One of the drawbacks of such double seal arrangements is the
limitation on the maximum capacity of the tank. Each of these large
diameter storage tanks is essentially full when the second seal is
just below the top of the wall. As such, as much as four feet
vertical feet of capacity is unavailable. For a tank having a
100-foot diameter, adding four additional vertical feet of capacity
translates to nearly 235,000 gallons of additional storage capacity
not being available for liquid storage so as to provide vapor
containment for the tank.
An alternative seal system that would reclaim the storage capacity
or reduce the space committed to vapor containment could translate
into significant dollars, especially for a storage terminal that is
paid to store hydrocarbons. Additional storage capacity could
translate into many dollars of added profit. This additional
capacity would be a welcome addition if capacity could be
incrementally increased without having to invest significantly in
building additional tanks. This may be especially welcome when
there is no available land to install new additional storage
tanks.
BRIEF SUMMARY OF THE DISCLOSURE
The invention more particularly relates to a process for expanding
the capacity of a floating roof cylindrical tank for storing
hydrocarbons. The process includes starting with a cylindrical tank
having a generally circular base with a periphery extending fully
around the circular base and generally cylindrical peripheral wall
extending vertically upward to a top edge and a floating roof with
two spaced apart seals arranged for sealing contact against the
generally cylindrical peripheral wall. A plurality of brackets are
provided up to the top of the floating roof where the brackets
include pre-drilled holes for attaching extension panels. A
plurality of extension panels are provided that are each thinner
and lighter weight than the generally cylindrical peripheral wall
up to the top of the floating roof where the extension panels
include pre-drilled holes to attach to the brackets and to attach
each panel to others of the plurality of panels. A sealant is
provided between each bracket and the generally cylindrical
peripheral wall and attaching each bracket to the generally
cylindrical wall end to end so as to create a sealed connection
between the brackets and the generally peripheral wall and to
provide a structure for which the extension panels may be attached
to the generally cylindrical peripheral wall. A sealant is provided
between each of the panels and the bracket and attaching each of
the panels to the bracket and to one another in an overlapping
arrangement where the panels overlap at least part of the bracket
and where at least part of each panel overlaps with other panels
with sealant between where they overlap such that when the panels
are attached to the brackets they form a generally cylindrical wall
extension extending upwardly from the generally cylindrical wall
such that the upper of the two seals on the floating roof may move
vertically with the floating roof and maintain a sealed vapor space
as the seal passes above the top edge of the generally cylindrical
peripheral wall and into contact with the panel extensions sealed
together and to the generally cylindrical peripheral wall.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention and benefits
thereof may be acquired by referring to the follow description
taken in conjunction with the accompanying drawings in which:
FIG. 1 is a perspective view of a conventional hydrocarbon storage
tank with a floating top;
FIG. 2 is a fragmentary cross section elevation view of the seal of
the floating top of a hydrocarbon storage tank shown with the
conventional arrangement with two vertically spaced apart seals
positioned against the interior peripheral wall of the storage
tank; and
FIG. 3 is a fragmentary elevation view similar to FIG. 2, but
showing a simple and inexpensive extension modification to the tank
according to the present invention that allows the floating top to
rise higher in the tank while containing the liquid hydrocarbons
inside the tank with the spaced apart double seal for vapor
containment;
FIG. 4 is an exploded fragmentary perspective view of a hydrocarbon
storage tank showing the extension for creating added storage
capacity in a form for being assembled and installed to an existing
hydrocarbon storage tank while in service; and
FIG. 5 is an enlarged fragmentary cross-sectional view showing a
preferred arrangement for adding a seal extension according to the
present invention.
DETAILED DESCRIPTION
Turning now to the detailed description of the preferred
arrangement or arrangements of the present invention, it should be
understood that the inventive features and concepts may be
manifested in other arrangements and that the scope of the
invention is not limited to the embodiments described or
illustrated. The scope of the invention is intended only to be
limited by the scope of the claims that follow.
As shown in FIGS. 1 and 2, a conventional hydrocarbon storage tank
is generally indicated by the number 10 having a generally circular
base, a cylindrical peripheral wall 20 extending up from the base
and having a top comprising a floating roof 12. The cylindrical
peripheral wall 20 is typically made of steel and is fabricated to
hold a very high volume of liquid hydrocarbons L such as crude oil,
gasoline, diesel, naphtha and a host of other intermediate and
finished hydrocarbon liquids. While such tanks may be made in just
about any dimension, it is typical for such storage tanks to be
large with a diameter in the range of 100-foot diameter and in
excess of 30 feet tall or deep.
The floating roof 12 is arranged to float on the surface of the
liquid contents of the tank 10 using flotation pontoons or the like
while raising and lowering as the liquid level changes. The reason
to have a floating roof 12 is to minimize the vapor space between
the surface level and the bottom of the floating roof 12. Vapors
are hazardous, so minimizing the volume of vapor with in a
hydrocarbon storage tank is safer, preferred and typically required
by environmental regulations.
Focusing on FIG. 2, the floating roof 12 includes a sealing system
engaged with the cylindrical peripheral wall 20. The sealing system
includes two spaced apart seals where a primary seal 13 is
positioned at the peripheral edge of the floating roof 12 to engage
the peripheral wall 20. A second seal 14 is positioned 18 or more
inches above the primary seal 13 although it is more conventional
that these two seals 13 and 14 are spaced apart by two to three
feet and as much as four feet apart. The second seal 14 is oriented
like the main seal to engage against the inside surface of the
peripheral wall 20 vertically above the primary seal 13 and move
vertically within the cylindrical wall 20. The two seals 13 and 14
seal the vapor space from the open atmosphere preventing
hydrocarbon emissions and together to contain the hydrocarbons. The
primary seal 13 and the second seal 14 are made of flexible
material, typically of a hydrocarbon resistant rubber so that they
slide along and seal against the inside of the cylindrical wall 20
flexing to follow the contour of the cylindrical wall 20 and
accommodate any reasonable shifting of the floating roof due to
unequally distributed weight from workers or equipment on the
floating roof 12. The roof typically has a shape such as with
sloping roof segment 16 to maintain outward pressure of the second
seal 14 against the wall 20
FIGS. 1 and 2 show the conventional floating roof technology for
liquid hydrocarbon storage tanks in use around the world. The
invention relates to an improvement to such hydrocarbon storage
tanks that simply and very inexpensively increases that available
storage capacity of an existing tank by about the vertical spacing
between the primary seal 13 and the second seal 14. The point that
was observed by the inventors is that both seals need to engage the
peripheral wall making the highest permissible liquid level be
indicated by the dotted line F in FIG. 2 even though the top of the
peripheral wall is indicated by the dotted line T. The difference
between dotted line T and dotted line F represents a significant
difference in capacity within the tank. But, the upper portion of
the cylindrical wall 20, where only the second seal 14 ever
impinges, does not have to be as structurally strong as the rest of
the cylindrical wall 20. The weight of the liquid is never imposed
on that upper portion between the full level L and the top T. While
the dimension and strength of the cylindrical wall of an existing
storage tank is strong top to bottom, it is sufficiently strong to
hold the weight of the liquid right to the top T of the tank 10.
For example, the wall 20 of storage tank 10 is typically at least
1/4 inch thick carbon steel at its top and often thicker and
certainly thicker at lower course heights of storage tanks. Being
strong enough to hold liquid, all that is needed is an extension
that can provide a vapor seal for second seal 14 to engage.
Turning now to FIG. 3, with an inexpensive extension 21 projecting
upwardly from the top of the peripheral wall 20, the full liquid
level or highest permissible level F is much closer to the top T of
the peripheral wall 20 as shown by the new full level F just below
the top T of the tank 10. This creates additional volume capacity
that is roughly equal to the spacing between the two seals 13 and
14 taking into consideration the area under the roof 12. This
represents a significant gain in storage capacity. For example, in
a storage tank have the spacing between the primary seal 13 and the
second seal 14 of 2 feet with tank diameter of 100 feet, the volume
that can be gained by allowing the liquid level to approach the
true top of the tank T would create more than 117,000 gallons of
additional capacity. For a facility that does not own hydrocarbons,
but only charges others for storage of their hydrocarbons, this
additional capacity gained in one storage tank can represent a
significant financial opportunity. Once the cost of installing the
extension has been incurred, there is essentially no further cost
for storing additional hydrocarbons and therefore charging
additional storage fees.
Focusing now on the inventive lightweight extension 21 as shown in
FIGS. 3, 4 and 5 and as envisioned the inventors, the second seal
14 is allowed to float above the top of the peripheral wall 20 but
still keep the vapors inside the storage tank 10 separated from the
atmosphere. The second seal 14 would continue to function quite
satisfactorily while moving vertically up and down along the light
weight sealing extension 21. The extension 21 extends vertically to
a level above the top T of the storage tank 10 to a height
preferably at least the distance between the two seals 13 and 14.
The extension is preferably made of stainless steel and is
preferably a thin gauge of between 0.010 inches up to 1/8 inch but
would more preferably be between 0.020 and 0.050 inches thick.
Alternatively, the extension 21 may be plastic, aluminum or other
lightweight metal. The extension 21 would not need to be permanent,
but once installed, it is unlikely to be removed except for
maintenance or repairs.
Focusing now on an example installation for a lightweight extension
that does not include welding or drilling on the existing storage
tank that is in service (with hydrocarbons stored in the tank while
the extension is being installed). A preferred attachment method is
shown in FIGS. 4 and 5 where the extension includes a plurality of
thin panels 25 that are arc shaped comparable to the radius of the
circular arc of the peripheral wall 20 of the storage tank 10. Each
of the panels includes pre-drilled holes 27 vertically along each
end which, when aligned allows the panels 25 to overlap with one
another. The overlapping ends are arranged to be bolted together
or, more preferably, to be riveted together. An elastomeric sealant
is applied between the sections 25 where they overlap to create an
effectively continuous circumferential extension at the top of the
peripheral wall 20. The panels 25 also have a horizontal row of
pre-drilled holes 28 along the lower portion so that they may be
mounted to the top of the peripheral wall 20 by a series of spring
brackets 22. The horizontally arranged pre-drilled holes 28 are
arranged to align with pre-drilled holes 29 in spring brackets 22.
More specifically, as shown in FIG. 5, the spring brackets 22
include a vertical segment 22A against which the panels 25 may be
attached using rivets 26 through horizontal pre-drilled holes 28
and 29. The spring brackets 22 include a shape to attach to and
extending around flange 20A at the top of the peripheral wall 20 of
the existing storage tank 10. This flange 20A is conventional at
the top of the peripheral wall 20 where it extends outwardly to
strengthen or reinforce the main body of the peripheral wall 20.
The flange 20A is sufficiently strong to support a modest (4
vertical feet upwardly is not excessive) lightweight extension
comprised of panels 25. The spring brackets 22 are preferably
formed of bent sheet steel to form a channel that slips over the
flange 20A with a compression grip on both top and bottom of the
flange 20A.
The attachment of the spring bracket 22 is best shown in FIG. 5
where it can be seen that the vertical segment 22A extends
vertically from the top of the peripheral wall 20 of the storage
tank 10. The vertical segment 22A extends from a top horizontal
segment 22B formed as a bend in a common sheet of thin stainless
steel. The top horizontal segment 22B lies flush on top of the top
surface of the flange 20A while an end segment 22C extends around
the outer periphery of the flange 20A and holds a bottom horizontal
segment generally flush against the bottom of the flange 20A. The
bends formed in the thin sheet of stainless steel are preferably
exaggerated so that the top horizontal segment 22B and bottom
horizontal segment 22D squeeze against the flange 20A. The panels
25 are attached in an overlapping manner with the vertical segment
22A such that the inside face 25A of the panel 25 is nearly flush
with the inside face 20B of the peripheral wall 20 and so that the
second seal 14 may slide from the inside face 20B up to the inside
face 25A of the extension 21 without breaking sealing contact and
maintaining the vapor space closed from the outside
environment.
While the spring brackets are preferably attached end to end to
extend fully around the peripheral wall 20, preferably they do not
overlap each other as some small space may be left between the ends
for adjustments during the installation process. These small gaps
are preferably bridged by a panel 25 to minimize potential leaks
such that the joints of the panels 25 are offset relative to the
joints in the spring brackets 22. Sealing materials, such as an
elastomeric, paste or putty, is preferably applied with the panels
25 attach flush to the vertical segments 22A.
In a manner similar to the attachment of the panels 25 end to end,
sealing compound such as elastomeric sealer is preferably applied
before the spring bracket is slipped on to the flange 20A. The
spring bracket includes a vertical segment extending upwardly to
the top of the channel section with a series of pre-formed holes
for attachment of the panels that also have the pre-formed holes.
Elastomeric sealer is also applied to the overlap of the vertical
section with the panels.
The process of installing the extension 21 begins by providing
spring brackets and extension sections 25 up to the top of the
floating roof. The sections 25 and spring brackets 22 are
preferably light enough to be carried up the stairs by human
personnel and not require heavy lifting equipment, like a crane or
construction forklift, to lift the sections to the top of the tank
10. Sealing compound is applied to the top of the flange 20A and
then spring brackets 22 are slipped over the flange 20A one by one
in an end-to-end arrangement extending fully around the periphery
of the storage tank 10 with the respective vertical segments 22A of
each of the spring brackets 22 being positioned in near alignment
with the inner face 20B of the peripheral wall 20. With the spring
brackets 22 attached, the panels 25 are then attached to the
vertical segments with sealing compound added between each flat
overlying face of the panels 25 and vertical segments 22A until the
extension 21 is fully complete around the peripheral wall 20. After
passing inspections, the liquid level in the storage tank 10 may be
raised such that floating roof 12 may float higher within the
peripheral wall 20 while lifting the second seal 14 above the top T
of the peripheral wall 20 and into contact with the extension
21.
In closing, it should be noted that the discussion of any reference
is not an admission that it is prior art to the present invention,
especially any reference that may have a publication date after the
priority date of this application. At the same time, each and every
claim below is hereby incorporated into this detailed description
or specification as additional embodiments of the present
invention.
Although the systems and processes described herein have been
described in detail, it should be understood that various changes,
substitutions, and alterations can be made without departing from
the spirit and scope of the invention as defined by the following
claims. Those skilled in the art may be able to study the preferred
embodiments and identify other ways to practice the invention that
are not exactly as described herein. It is the intent of the
inventors that variations and equivalents of the invention are
within the scope of the claims while the description, abstract and
drawings are not to be used to limit the scope of the invention.
The invention is specifically intended to be as broad as the claims
below and their equivalents.
* * * * *